Does Serotonin Influence Aggression? Comparing Regional Activity before and during Social Interaction

Abstract

Serotonin is widely believed to exert inhibitory control over aggressive behavior and intent. In addition, a number of studies of fish, reptiles, and mammals, including the lizard Anolis carolinensis, have demonstrated that serotonergic activity is stimulated by aggressive social interaction in both dominant and subordinate males. As serotonergic activity does not appear to inhibit agonistic behavior during combative social interaction, we investigated the possibility that the negative correlation between serotonergic activity and aggression exists before aggressive behavior begins. To do this, putatively dominant and more aggressive males were determined by their speed overcoming stress (latency to feeding after capture) and their celerity to court females. Serotonergic activities before aggression are differentiated by social rank in a region-specific manner. Among aggressive males baseline serotonergic activity is lower in the septum, nucleus accumbens, striatum, medial amygdala, anterior hypothalamus, raphe, and locus ceruleus but not in the hippocampus, lateral amygdala, preoptic area, substantia nigra, or ventral tegmental area. However, in regions such as the nucleus accumbens, where low serotonergic activity may help promote aggression, agonistic behavior also stimulates the greatest rise in serotonergic activity among the most aggressive males, most likely as a result of the stress associated with social interaction.

Melanin-based skin spots reflect stress responsiveness in salmonid fish

“…Our results support the idea that differing dynamics of the stress response may be a consistent and partly inherited trait. Other studies have indicated that this trait may be a cause, as much as a consequence, of social status (Pottinger and Pickering, 2001;Øverli et al 2004;Summers et al 2005). Salmonid fish can exhibit physiological colour change during stress; subordinate individuals e.g.…”

Effects of season, testosterone and female exposure on c-fos expression in the preoptic area and amygdala of male green anoles

“…Perhaps more likely, though, is a connection to aggression. In anole lizards, subordinate (less aggressive) males have higher baseline serotonergic activity in the AMY than their more aggressive counterparts (Summers et al, 2005). Plasma T increases with aggressive encounters in anoles (Yang and Wilczynski, 2002).…”

Rapid neuroendocrine responses evoked at the onset of social challenge

“…Increased amygdalar serotonergic activity is associated with social stress across vertebrate taxa [10], and is known to enhance mammalian hypothalamic-pituitary-adrenal (HPA) axis activity and glucocorticoid release [51,52]. The rapid increases in A. carolinensis amygdalar DA levels with social threat occurred in areas homologous with the central, lateral and medial nuclei of the mammalian amygdala [23][24][25].…”

“…In particular, alterations to dopamine (DA) and serotonin (5-HT) function within discrete basal ganglia and mesolimbic nuclei, including key forebrain regions such as the nucleus accumbens (NAc) and amygdala, occur during or immediately following production of agonistic social behavior [4,[8][9][10]. Enhanced DA activity in the NAc normally mediates expression of motivated or goal-directed behaviors during both rewarding and aversive situations [11,12], while increased amygdalar 5-HT activity is associated with stress, fear and anxiety [13][14][15][16][17].…”

“…The lizard Anolis carolinensis has become well established as a model for examining the effects of agonistic social stress on neuroendocrine activity [5,9,10]. During the early stages of interaction between A. carolinensis males, conveyance of aggressive intent is facilitated by the darkening of postorbital skin (known as the "eyespot"), caused by sympathetic catecholamine activation of β-adrenergic receptors [6,18].…”